Manufacturers of mobile communication terminals are currently seeking to miniaturize them as much as possible whilst preserving optimum functional ergonomics.
This optimization of the size of the terminals, of which FIG. 1 is a diagrammatic side view, has impelled manufacturers to reduce their thickness.
A mobile terminal comprises a casing 10 in which are disposed various components such as a battery 20, a keypad 30, a screen 40 and a sound-reproducing transducer 60 connected to a printed circuit 50.
The sound-reproducing transducer or sound transducer 60 is adapted to transform electrical signals supplied to it into sound waves and vice-versa.
The sound transducer 60 may fulfill a plurality of functions such as those of earpiece, loudspeaker, ringer and vibrator.
The earpiece is essentially intended to be placed against the ear of a user when using the device to communicate, the ringer is used to alert the user to an incoming call or any other action, the loudspeaker enables sound reproduction at high volume for hands-free or ringer applications, for example, and the vibrator is used to alert the user discreetly to an incoming call through vibration of the earpiece.
To reproduce the sound waves, the sound transducer 60 consists of two distinct volumes defining a front acoustic cavity 61 and a rear acoustic cavity 62 the shapes and dimensions whereof must be adapted to allow sound reproduction of sufficient quality for the application for which the transducer is intended.
This sound reproduction is obtained by virtue of vibrations of a diaphragm that will be precisely defined hereinafter in the description of FIG. 3.
Moreover, the earpiece function necessitates a smaller component size than that required for a loudspeaker and ringer function which must emit sound at a greater volume. The volume occupied by the sound transducer 60 may not therefore be reduced beyond a certain limit imposed by the loudspeaker function.
Now, the current trend is to reduce the size and in particular the thickness of terminals.
Accordingly, the rear acoustic cavity 62 of the sound transducer 60 of current terminals has a volume of insufficient size and the space between the rear face of the transducer and the printed circuit is too small to allow sound reproduction of sufficient quality.
Inopportune damping of vibrations in the diaphragm of the sound transducer 60 occurs if the space between the rear face of the transducer and the printed circuit is less than 1 mm thick.
Those vibrations generating the sound, this leads to insufficient quality of sound reproduction.